Compatible mixtures of modified starch and polyvinyl alcohol

ABSTRACT

STARCH-POLYVINYL ALCOHOL (PVA) FORMULATIONS ARE PREPARED FROM AN ETHERIFIED DEPOLYMERIZED STARCH PRODUCT, WHICH CONSISTS ESSENTIALLY OF STARCH CONTAINING -COOX GROUPS, WHEREIN X IS A CATION SELECTED FROM NA+, K+, OR NH4+, IN THE AMOUNT OF 0.3 TO 3% BY WEIGHT BASED ON SAID PRODUCT OF -COONA, OR MOLAR EQUIVALENT OF -COOK OR -COONH4, SAID -COOX GROUPS BEING PRESENT AS STARCH -O-CH2-COOX, OR AS A MIXTURE OF STARCH -O-CH2-COOX AND STARCH -COOX, SAID MIXTURE CONTAINING AT LEAST 0.1% /COONA, OR MOLAR EQUIVALENT OF -COOK OR -COONH4, AS SAID   STARCH-O-CH2-COOX,   SAID STARCH PRODUCT BEING FURTHER CHARACTERIZED BY AN ALKALI FLUIDITY OF LESS THAN 95 AND ABOVE 5 AND BY BEING SUBSTANTIALLY FREE OF INORGANIC SALTS. THE FORMULATIONS OF THE STARCH PRODUCT WITH PVA ARE COMPATIBLE AND STABLE OVER A WIDE RANGE OF PROPORTIONS.

United States Patent O 3,767,604 COMPATIBLE MIXTURES OF MODIFIED STARCHAND POLYVINY L ALCOHOL Erling T. I-Ijermstad and Leonard J. Coughlin,Cedar Rapids, Iowa, assignors to Penick & Ford, Limited, Cedar Rapids,Iowa No Drawing. Original application July 15, 1969, Ser. No. 841,961.Divided and this application Oct. 29, 1971, Ser. No. 194,022

Int. Cl. C08d 9/06 US. Cl. 26017.4 ST 14 Claims ABSTRACT OF THEDISCLOSURE Starch-polyvinyl alcohol (PVA) formulations are prepared froman etherified depolymerized starch product, which consists essentiallyof starch containing COOX groups, wherein X is a cation selected fromNa+, K or NH in the amount of 0.3 to 3% by weight based on said productof COONa, or molar equivalent of COOK or COONH said COOX groups beingpresent as starchOCH COOX, or as a mixture of starchO-CH COOX andstarchCOOX, said mixture containing at least 0.1%-COONa, or molarequivalent of COOK or COONH as said said starch product being furthercharacterized by an alkali fluidity of less than 95 and above 5 and bybeing substantially free of inorganic salts. The formulations of thestarch product with PVA are compatible and stable over a Wide range ofproportions.

CROSS REFERENCE This application is a division of our co-pendingapplication Ser. No. 841,961, filed July 15, 1969 now US. Pat.3,652,542, issued Mar. 28, 1972.

BACKGROUND Starch has been used with polyvinyl alcohol (PVA) for anumber of years, particularly in adhesives and textile sizes. Theincorporation of PVA improves bonding strength, film strength andflexibility, grease and oil resistance, Water resistance, etc.Generally, the more highly hydrolyzed grades of PVA are used with starchin proportions up to 1 part of PVA to 3 parts of starch.

While PVA has been used commercially with starch for adhesives andtextile sizes, there has been very little success in developing mixturesof PVA and starch which give the desired improvement and areeconomically feasible. PVA is a relatively high cost material and it isneces sary to use an extender, such as starch, dextrin, casein, clay,calcium carbonate, etc., to lower costs. Starch would appear to be anideal extender because of its extremely low relative cost and itsability to form fairly strong and flexible grease and oil resistantfilms. However, attempts to formulate PVA-starch mixtures withsuflicient PVA to attain worthwhile improvement in sized paper have beenunsuccessful due to the tendency of starch and PVA to separate into a2-phase system when proportions of starch and PVA greater than about ofeither one with the other are dispersed in water. It would be desirableto use from 10% to 50% PVA in the PVA- starch mixture to obtainworthwhile improvement in paper sizes. Another effect higher ratios ofPVA to starch during paper sizing have is the rejection of one componentwhen the sized paper is passed through the rolls of a size press, thuschanging the ratio in the remaining size and causing a deterioration insized sheet properties on continued operation. For these reasons, therehas been very little commercial use of PVA-starch mixtures for papersizing, especially at paper size viscosity and concentration levels.

A great number of starch varieties, starch modifications, starchderivatives, and dextrins have been evaluated with PVA in attempts toovercome these deficiencies and develop formulations which will givesatisfactory performance at economically feasible proportions ofcomponents. Ordinary commercial starches such as unmodified starch,acid-thinned starch, or dextrins made from the common varieties ofstarch gave very poor performance. Oxidized starches andhydroxyethylated starches gave improved performance (Elvanol Brochure,Du Pont Co. 1967, p. 15) but negligible commercial success has resulted.The use of esterified or etherified starches containing carboxylradicals was suggested in 1957 in US. Pat. 2,808,380. These show someimprovement as do oxidized starches which also contain carboxyl groups.However, neither oxidized starches nor derivatized starch with carboxylradicals have been sufficiently suitable to result in commercialdevelopment of economically feasible, improved performance starch-PVApaper sizes. There has, therefore, been a definite need for a starchproduct which can be used with PVA in proportions up to 50% of eachwithout phase separation and rejection of components during size pressoperation.

SUMMARY This invention is based on the discovery that the compatibilityof starch with polyvinyl alcohol depends on a number of complex andinterrelated factors, including the degree of COOX substitution byetherification and/ or oxidation, the extent of depolymerization, andthe freedom of the product from inorganic salts. Using -COONa as thebase, the starch should contain from 0.3 to 3% by weight of the sodiumcarboxy groups (or molar equivalent of potassium or ammonium carboxygroups). The extent of depolymerization, as determined by alkalifluidity, should be such that the starch product has an alkali fluidityof less than and above 5. In addition, it is critical that the productcan substantially be free of inorganic salts, such as sodium chloride orsodium sulfate, which are frequently present in high concentrationsduring the etherification of starch.

The invention in its preferred embodiments includes other importantdiscoveries. While the starch product can be thinned or depolymerized byacids or enzymes, hypochlorite oxidation is preferred. It has been foundthat such oxidation not only thins the etherified starch to thenecessary fluidity, but also, under alkaline conditions, introducesadditional -COOX groups. Where the carboxyalkyl ether product isdepolymerized by acid, it has been discovered that a special treatmentis desirable to break any cross-links, which may be formed. Theresulting product will contain the COOX groups in the form ofstarchO(CH- COOX where n equals 1 or 2. Preferably, however, the productcontains the -'COOX groups in the form of a mixture of starchO-CH COOXand starchCOOX, the latter modification resulting from the hypochloriteoxidation.

The preferred substitution and alkali fluidity ranges, substituentgroups, salt content, and other criteria, will be described in thefollowing detailed specification. It will be understood that these formpart of the present invention, and provide the means for maximizing theadvantages of the invention.

DETAILED SPECIFICATION The starting material for the present inventioncan be any granule starch, such as the starches derived from corn,potatoes, waxy maize, tapioca, etc. These starches in their originalunmodified state are obtained in granular form, being cold waterinsoluble, and being subject to gelatinization on heating in water. Asis well known in the art, the granule structure of starch persists e'venduring such modification treatments as etherification, acidconversion tothin-boiling types of starch, and hypochlorite oxidation. The termstarch" is therefore used in its broad or generic sense in thisapplication as referring to any of the known varieties of starch.

In the practice of the present invention, the granule starch isetherified with a carboxyaikylating agent to introduce carboxyalkylether groups. Suitable carboxyaikylating agents are alkali metalmonochloracetate, alkali metal salt of 3-chloropropionic acid,acrylamide, and acrylonitrile. The etherification of granule starch tointroduce alkali metal carboxymethyl groups is described in US. Pat.2,773,057.

Alkali metal carboxyethyl groups are also effective in the presentinvention. These can be introduced into starch by reaction understrongly alkaline conditions, for example, in aqueous NaOH or KOHcontaining NaCl or Na SO to prevent starch swelling, with reagents suchas acrylamide, acrylonitrile, or 3-chlor0propionic acid. Ammoniumcarboxyalkyl starch ether groups are also effective. These can beintroduced by removing the alkali metal from alkali metal carboxyaikylstarch, for example, by ion-exchange, to form starch-O-(CH ),,COOH, thenneutralizing with ammonia to form starchO(CH COONH The resultingetherified starch is then subjected to depolymerization.Depolymerization of the etherified starch product is essential to obtainproducts which do not show phase separation when dispersed in water withhigh proportions of PVA at low viscosity levels. The depolymerizationcan be done by acids, for example, HCl or H 80 and the thinned productneutralized and washed free of salts on a filter or centrifugalequipment. The acid depolymerization is conducted in water suspensionsat temperatures below the swelling temperature of the etherifiedproduct. Sufficient acid to lower the pH to around 1.0 is added. LowerpH will give a faster rate of acid depolymerization. Oxidizing agentscan be used to depolymerize the etherified starch. These have theadvantage of increasing the anionic groups in the starch polymerstructure while at the same time thinning or depolymerizing to a lowviscosity level. Suitable oxidizing agents are hypochlorites, such assodium hypochlorite, persulfates, such as ammonium or alkali metalpersulfates, and peroxides, such as hydrogen peroxide or sodiumperoxide. Sodium hypochlorite is the preferred oxidizing agent and underalkaline conditions it is an effective thinner and contributesadditional sodium carboxy groups. The proportion of oxidizing agent usedcan vary widely, depending upon the reaction conditions, particularly,the pH of the starch suspension. Sodium hypochlorite used in aproportion range of from 1% to 6% available chlorine based on starchsolids, results in suificient depolymerization. The use of from 2% toavailable chlorine based 'on starch solids is preferred. Enzymes, forexample alpha amylase, can be used to depolymerize the etherifiedproduct in the gelatinized state. Very low proportions of these enzymes,such as .05 to .25 based on starch solids are efiective.

Following etherification and depolymerization, the starch is fiitered,and washed to a low salt content. As indicated above, the starch productshould be substantially free of inorganic salts. In general, thewater-soluble salt content should be less than 1.5% weight, andpreferably less than or at least not over 1.0% by Weight. The optimumrange is about 0.1 to 0.5%.

The degree of depolymerization can be specified in terms of the alkalifluidity of the depolymerized product. This viscosity measurement iscommonly used to characterize thin-boiling and oxidized starches in thecorn wet-milling industry. The method is described in Chemistry andIndustry of Starch 2nd Ed., by R. W. Kerr, Academic Press, N.Y. 1950, p.133-134.

Alkali fiuidities ranging from 5 to are suitable in the present process.Fluidities of from 30 to 90 are preferred. While it is convenient tofirst etherify the starch and then depolymerize it, the reverse sequencecan also be used in certain cases.

Since the foregoing depolymerization processes are well-known in theart, it will not be necessary to describe them further herein. Theoxidation of starch with alkaline hypochlorite is described in standardtreatises such as Chemistry and Industry of Starch, Kerr, AcademicPress, Inc. (2nd 1950). In addition to the depolymerization, it isgenerally accept that COOX groups are introduced into the starch. TheseCOOX groups are formed from the carbon atoms of the glucose unit andoxidized starch is designated in this specification as starch-COOX.Alkaii metal or ammonium carboxyalkyl ethers of starch are hereindesignated as starch-O(CH ),,COOX. (n'=1 or 2.) In a preferredembodiment of the present invention, the etherified depolymerized starchproduct contains a mixture of starch-OCH COOX and starchCOOX. Further,the mixture contains at least 0.1% COONa, or a molar equivalent of COOK,or COONH in the form of starch-OCH -COOX. When the starch productcontains a total of 0.4 to 2.0% by weight of COONa (or molar equivalentgroup) as preferred, optimum benefits are obtained when the starchproduct contains at least 0.2% of COONa (or equivalent group) asstarchOCH COONa. Consequently, when the starch is to be thinned byhypochlorite oxidation, as is preferred, the amount of COOX groupsintroduced in the etherification can be kept to a lower level, thestated ranges applying to the amount of such groups introduced byetherification plus the amount introduced by the hypochlorite oxidation.

It has been discovered that when carboxyalkyl starches, such asetherified starch having sodium carboxy radicals in the attached group,are acid-depolymerized, the starch becomes resistant to gelatinizationto a dispersed, lowviscosity state. This appears to be due to theformation of ester cross-links between the carboxyls and the hydroxylsof the starch under conditions of high acidity. It has been furtherdiscovered that this cross linking effect can be overcome simply byraising the pH of the acid-converted starch ether suspension to around8.5-9 or higher (viz pH 85-105) and steeping for a short period of time,such as /2 to 2 hours. The product can be dewatered and washed in thealkaline state or neutralized and dewatered and washed. The alkalisteeped product disperses readily to a low viscosity paste on cooking,indicating that the cross-links are removed.

It will be understood that whatever method of depolymerization isemployed, the resulting product will have an alkali fluidity within theranges stated above. As used herein, the term alkali fluidity refers tothe standard starch test, as described for instance, in Chemistry andIndustry of Starch, Kerr, pages 133-134 (2nd ed., 1950, Academic Press,Inc., N.Y.).

Etherified depolymerized starch products produced as described above canadvantageously be employed in combination with polyvinyl alcohols of thekind which have heretofore been used as sizes or adhesives. In theindustry, such polyvinyl alcohols are usually specified in terms ofdegrees of polymerization (unit average molecular weight based on CHCHOH monomer) and degree of hydrolysis (mole percent). In general,suitable polyvinyl alcohols have a degree of polymerization ranging fromabout 300 to 1900, and a degree of hydrolysis greater than 88%,preferably greater than 98%. For use as sizes, the preference is forsubstantially completely hydrolyzed products (98.8-100% hydrolyzed).Depending on the use to be made of the PVA, the molecular weight can bevaried. For paper size applications, a preferred degree ofpolymerization is from about 300 to 1400, and espe cially advantageousare PVAs of 1000-1400. Polyvinyl alcohols of this character areavailable as dry powders,

being sold for example, by E. I. du Pont de Nemours & C0,. Wilmington,Del. under the trademark, Elvanol. Suitable products are Elvanol 72-60,Elvanol 71-30 and Elvanol 70-05.

According to the present invention, it is preferred to employ at leastparts by weight of polyvinyl alcohol per 90 parts of the modifiedstarch. The compatibility of modified starch as prepared in accordancewith the present invention permits much higher proportions of polyvinylalcohol, up to 60 parts of PVA per 40 parts of modified starch. For useas a paper size, the preferred range is about parts by weight ofpolyvinyl alcohol per 85 parts of modified starch up to 50 parts of PVAper 50 parts of the modified starch. The granule starch and PVA powdercan be dry blended in suitable mixing equipment to produce a dry mixturewhich can then be used to form stable size or adhesive compositions. Themixture, or the separate ingredients, can be heated in water at atemperature and for a time sutficient to gelatinize the starch anddissolve the PVA. Usually, heating at about 190-200 F. for 30 minuteswill be sufficient to complete the formulation. It will be understoodthat the 1 water serves as a carrier, and that the amount of water willbe adjusted to produce a complete formulation of the desired viscosity.For use as a paper size, formulations having a Dudley viscosity of about40-60 seconds at 150 F. are preferable. The Dudley viscosity is astandard test in the art, being described, for example, in Chemistry andIndustry of Starch, Kerr, pages 121-122 (2nd ed., 1950, Academic Press,Inc., N.Y.).

This invention is further illustrate by the following specific examples.Unless otherwise designated, the polyvinyl alcohol (or PVA) referred toin the examples is a fully hydrolyzed (98.8% or higher) polyvinylalcohol having a degree of polymerization ranging from 300 to 1400, suchas Du Ponts Elvanol No. 71-30 (99-100% hydrolyzed; 1200 unit averagemolecular weight).

Example 1 A low-substituted sodium carboxymethyl starch, containingapproximately 1% by weight of COONa groups, was suspended in water in40% solids concentration. The pH of the suspension was adjusted toaround 1.0 with H SO and the suspension was agitated at 120 F. for 24hours. The acid-converted product had an alkali fluidity of 90 asmeasured by the test described in Chemistry and Industry of Starch, 2nded., by R. W. Kerr, Academic Press, N.Y., 1950, p. 133.

Acid-converted 90 alkali fluidity sodium carboxymethyl starchsuspensions were neutralized to diflerent pH levels for 1-3 hours at110-115 F. All of the suspensions were then neutralized to pH 7.0,dewatered on a filter, and washed free of salts. The purified productswere dried at room temperature.

The starches were made up in 30% dry substance concentration in water,readjusted to pH 7.0 and run in a Corn Industries viscometer with awater bath temperature of 210 F. After 30 minutes of cooking in theviscometer, Brookfield viscosities were determined at 190 F. The resultsof steeping the acid-converted sodium carboxymethyl starches atdifferent pH levels before final neutralization and purification aregiven below in Table A:

The Corn Industries viscometer and Brookfield viscometertests aredescribed in Methods in Carbohydrate Chemistry by Whistler, vol. IV,Academic Press, N.Y. (1965), pages 117 and 121.

Example 2 l0 Unmodified starches were reacted in an alkaline suspensioncontaining sodium chloride or sodium sulfate as a swelling inhibitorwith varying proportions of sodium monochloracetate to form sodiumcarboxymethyl starch 15 ethers. The suspensions were neutralized and thepH adjusted to around 1.0 with HCl or H SO The acid conversions werecontinued until the products showed alkali fluidities of 80-90. Thesuspensions were adjusted to pH 9.0 with Na CO and held at this pH for1-2 hours, then 0 neutralized to pH 7.0 with HCl, dewatered, washed freeof salts on a filter, and dried. The products were analyzed for CO0 Nacontent. These products and other types of starch were then cooked withthe PVA (99% hydrolyzed) in a 1:1 ratio, at around 15% total solidsconcentration 25 at 190 F. for minutes and the viscosity of thedispersions adjusted to Dudley Pipette viscosities of -50 sec., at 150F. by dilution. The dispersions were allowed to stand for 24-48 hours todetermine phase separation. The results are tabulated below in Table B:

1 The Alkaline Fluidity and Dudley Hot Paste viscosity tests aredescribed in Chemistry and Industry of Starch, by Kerr, 2nd Ed.,Academic Press, N.Y. (1950), pages 121-122, and

1 61 starch to PVA dispersion (Dudley viscfi' 40-50 sec. at

3 No conversion.

Example 3 Following the procedure of Example 2, potato starch,

waxy maize and tapioca starches were prepared as acidconverted, sodiumcarboxymethyl starches. The results are shown below in Table C.

TABLE 0 Phase separation on Percent standing Base GOONa Alkali 24-28starch content fluidity hours 0.57 8 Slight. 1.00 89 None.

0.52 19 Do. Tapioca 0. 72 89 Do.

1 :1 starch to PVA dispersion (Dudley visc. 10-50 sec. at 150 E).

Example 4 Unmodified starches of different varieties were reacted in analkaline suspension containing sodium chloride or sodium sulfate as aswelling inhibitor with varying proportions of sodium monochloracetateto introduce sodium carboxymethyl ether groups into the starch. Thesuspensions were then neutralized to pH 7.0 with acid. Sufficient sodiumhypochlorite solution, analyzing around 6- 7% available chlorine and 2%NaOH, to depolymerize the starches to -90 alkali fluidity, was added andthe 75 suspension agitated at F. for 18-20 hours. Proportions ofavailable chlorine based on starch solids ranged from 45%.

The suspension were neutralized to pH 7.0, dewatered on a filter, washedfree of salts, and dried. The oxidatively depolymerized sodiumcarboxymethyl starches were analyzed for CO Na content and alkalifiuidities were determined. The starches were tested in starch-PVAdispersions as described in Example 2. The results are given below inTable D:

TABLE D O O ONa content From Na From Na Alkali Phase chloracctatehypochlorite fluidity separation Base reaction, reaction, after onstanding starch percent percent conv. 18 hours Corn None 1. 09 9OSevere.

Do 0. 13 0. 65 89 None.

Do 0.15 0. 67 88 Do.

Do 2. 28 0.51 87 D0. Potato 0. 57 1.0 92 D0. Waxy maize... O. 52 0. 8490 Do, Tapioca... 0. 72 1.28 92 Do.

1 1:1 starch to PVA dispersion (Dudley visc. 40-50 sec; at 150).

Example 5 A low-substituted sodium carboxymethyl starch, containing1.32% sodium carboxymethyl groups, was enzyme-converted to a lowviscosity according to the following procedure. The starch was slurriedin water with PVA (99% hydrolyzed) in 1:1 ratio at 15% total solidsconcentration. Two-tenths percent calcium acetate based on starch wasadded. The slurry was adjusted to pH 7.0 with sodium carbonate and 0.05%of a bacterial alpha amylase concentrate (Amyliq, Waller-stein Co.) wasadded. The slurry was heated to 170 F. and held at this temperature for15 minutes, then heated with steam to 190200 F. and held at thistemperature for 30 minutes.

The enzyme-converted dispersion of sodium carboxymethyl starch and thePVA was adjusted to a Dudley Pipette viscosity of 4050 seconds at 150 F.No phase separation occurred on standing for 48 hours. Regular cornstarch converted to the same degree with the same enzyme treatmentshowed severe phase separation when under the conditions of the test.

Example 6 Properties of paper sized with dispersions of de-polymerizedsodium carboxymethyl starch with PVA.

(A) Oil and grease holdout.-Using TAPPI Method T454-TS66 on a commercialwhite patent-coated board, the following values were obtained at anadd-on rate of 3.1 lbs. per 1000 sq. ft. of board.

The board used was surface-sized as indicated above, and the penetrationtime determined. The TAPPI Method citation is, Turpentine Test forGrease Resistance of Paper, Technical Assn. of Pulp & Paper Industry,New York, N.Y. The PVA was Du Pont Elvanol 71-30. The above data showthe greatly improved grease and oil holdout with depolymerized sodiumcarboxymethyl starch and PVA, especially with equal parts of PVA andstarch, as compared with hydroxyethyl corn starch which has beenconsidered effective for this purpose.

(B) Porosity.-Bleached paper coating base stock was treated with a clearsize having a ratio of one part PVA (Du Pont Elvanol 71-30) to threeparts of depolymerized sodium carboxymethyl starch similar to that usedin (A) above. It showed a substantial increase in Gurley Porosity valueas compared with that given by a conventional hydroxyethylated cornstarch sizing formulation. Acid depolymerized sodium carboxymethylstarch with PVA also showed improved porosity values. This improvementin porosity indicated that a more continuous and effective film had beenapplied. The citation of the Gurley test is, Standard Analytical MethodT 460-OS68; Air Resistance of Paper, Technical Assn, of Pulp & PaperIndustry, New York, N.Y.

Example 7 In Table D of Example 4, a modified corn starch and its methodof preparation are described, which contained l.l5% COONa from thechloroacetate reaction and 0.67% from the hypochlorite reaction. Asubstantially similar product in the form of ungelatinized granulestarch can be dry-blended with PVA powder to produce commercial productsfor admixture with water to form stable paper size compositions. The PVAcan be Du Ponts Elvanol 7l30. Preferably, the starch granules andparticles of PVA are similarly sized to minimize separation of themixture. The modified starch granules and PVA powder are dry-blended toa uniform mixture in suitable mixing equipment, according to thefollowing proportions:

Parts starch y w The foregoing mixtures can be combined with water insuitable proportions (10-15% solids, usually about 12% solids) toproduce a Dudley viscosity, after heating, within the rang from 40-60seconds at F. A suitable heating procedure, which is preferably carriedout with mild agitation, is -200 F. for 30 minutes. This will assuregelatinization of the starch and solution of the PVA. The resulting sizeformulation can then be checked for Dudley viscosity, and adjusted ifnecessary, before ap plication to the paper.

Etherified depolymerized starch products equivalent in many ways to theproducts described in the foregoing specification can be obtained byfirst etherifying the starch with a reagent introducing carboxyethylgroups, and forming starchO-CH CH COOX. These compounds can be regardedas homologues of the compounds previously described, and all of theranges and limitations previously set forth are applicable thereto.Various reagents can be used to form carboxyethyl starch, as is wellknown in the art. For example, the starch can be reacted withacrylonitrile under alkaline conditions, or with acrylamide, or with amonochloropropionate reagent such as sodium monochloropropionate. Thefollowing example is illustrative:

Example 8 Unmodified corn starch was reacted with the sodium salt of3-chloropropionic acid to introduce sodium carboxyethyl groups into thestarch.

Unmodified corn starch in a 40.7% dry substance concentration wastreated with a mixture of 30% sodium hydroxide and 26% sodium chloridecontaining 3% by weight of NaOH based on starch solids and 8% by weightof NaCl based on initial water in the suspension. The salt-alkalimixture was added with vigorous agitation of the suspension to preventlocalized swelling of the starch at the point of addition before thealkali was distributed throughout the suspension and 4.82% by weight ofthe sodium salt of 3-chloropropionic acid based on starch solids wasadded. An aliquot of the suspension was titrated with standard acidsolution and the suspension was agitated at 115 F. until 4.3% by weightof sodium chloropropionate based on starch solids has been bydroylzed,as indicated by the suspension titer. The suspension was thenneutralized and acid-converted with H at 110 F. until the starch producthad an alkali fluidity of 78 as measured by the test described inChemistry and Industry of Starch, 2nd Ed., by R. W. Kerr, AcademicPress, N.Y., 1950. The suspension was neutralized with Na CO solution,dewatered on a filter, washed substantially free of salts, and dried.

The purified product containing sodium carboxyethyl groups Was cookedwith PVA (99% hydrolyzed) in a 1:1 ratio, at around 15% total solidsconcentration at 190 F. for 30 minutes and the viscosity of thedispersion adjusted to a Dudley Pipette viscosity of 4050 seconds at 150F. by dilution. The dispersion showed greatly improved stability andresistance to phase separation on standing 48 hours as compared with 90fluidity acid or hypochlorite converted corn starch which showed severephase separation under the conditions of the test.

Example 9 Unmodified corn starch was reacted with acrylamide understrongly alkaline conditions to introduce sodium carboXyethyl groupsinto the starch.

Unmodified corn starch in a 40.7% dry substance concentration wasuntreated with a mixture of 30% sodium hydroxide and 25% sodium chloridecontaining 3% by weight of NaOH based on starch solids and 8% by weightof NaCl based on initial water in the suspension. The salt-alkalimixture was added with VigOI'Ous agitation of the suspension to preventlocalized swelling of the starch at the point of addition before thealkali was distributed throughout the suspension and 2.4% by weight ofacrylamide based on starch solids was added. The suspension was agitatedfor several days at 115 F. then neutralized and acid-converted with H 80until the starch product had an alkali fluidity of 73 as measured by thetest described in Chemistry and Industry of Starch 2nd Ed., by R. W.Kerr, Academic Press, New York, N.Y. 1950. The suspension was thenneutralized with Na CO solution, dewatered on a filter, washedsubstantially free of salts, and dried.

The purified, depolymerized product containing sodium carboxyethylgroups was cooked with -PVA (Elvanol 7130 of Du Pont) in a 1:1 ratio, ataround 15% total solids concentration at 190 F. for 30 minutes and theviscosity of the dispersion adjusted to a Dudley Pipette viscosity of40-50 seconds at 150 F. by dilution. The dispersion exhibited greatstability on standing and negligible phase separation occurred during 48hours.

We claim:

1. A compatible, stable formulation of polyvinyl alcohol and starchconsisting essentially of:

(a) an aqueous carrier;

(b) a polyvinyl alcohol dissolved in said carrier having a degree ofpolymerization ranging from about 300 to 1400 and a degree of hydrolysisgreater than 88%; and

(c) a modified starch dispersed in said carrier consisting essentiallyof starch containing COOX groups, wherein X is a cation selected fromNa+, =K+, or NH in the amount of 0.3 to 3% by Weight 10 based on saidmodified starch of COONa, or molar equivalent of COOK or COONH said COOXgroups being present as starchOCH COOX or as a mixture of starch-OCHCOOX and starch-COOX, said mixture containing at least 0.1% COONa, ormolar equivalent of COOK or COONH as starch-O-CH -COOX, said modifiedstarch being further characterized by an alkali fluidity of less than 95and above 5 and by being substantially free of inorganic salts; saidformulation containing at least 10 parts by weight of said polyvinylalcohol per parts of said modified starch up to 60 parts of saidpolyvinyl alcohol per 40 parts of said modified starch.

2. The formulation of claim 1 wherein said COOX groups are present assaid mixture.

3. The formulation of claim 1 wherein said COOX groups are -COONagroups.

4. The formulation of claim 1 wherein said COONa groups are present inan amount of 0.4 to 2.0% by weight and said modified starch contains atleast 0.2% COONa as starchOCH COONa, and said modified starch is furthercharacterized by an alkali fluidity of 30 to 90 and by water-solublesalt content of less than 1.5% by weight.

5. The formulation of claim 1 characterized by the further fact that itcontains at least 15 parts by weight of said polyvinyl alcohol per 85parts of said modified starch up to 50 parts of said polyvinyl alcoholper 50 parts of said modified starch.

6. The formulation of claim 1 further characterized in that saidpolyvinyl alcohol has a degree of polymerization ranging from about 300to 1400 and a degree of hydrolysis of at least 98%, and in that saidformulation has a Dudley viscosity of 40 to 60 seconds at 150 F.

7. A compatible, stable formulation of polyvinyl alco- {101 2nd starchfor use as a paper size consisting essential- (a) an aqueous carrier;(b) a polyvinyl alcohol dissolved in said carrier having a degree ofpolymerization ranging from about 300 to 1400 and a degree of hydrolysisgreater than and (c) a modified starch dispersed in said carrierconsisting essentially of starch containing COOX groups, wherein X is acation selected from Na K+, or NH in the amount of 0.3 to 3% by weightbased on said modified starch of COONa, or molar equivalent of COOK orCOONH said COOX groups being present as starchOCH COOX or as a mixtureof starchOCH COOX and starch-COOX, said mixture containing at least 0.1%COONa, or molar equivalent of COOK or COONH as starchO-CH COOX, saidmodified starch being further characterized by an alkali fluidity of 30to 90 and by being substantially free of inorganic salts;

said formulation containing at least 15 parts by weight of saidpolyvinyl alcohol per 85 parts of said modified starch up to 50 parts ofsaid polyvinyl alcohol per 50 parts of said modified starch, and havinga Dudley viscosity of 40 to 60 seconds at F.

8. The formulation of claim 7 wherein said COOX groups are COONagroupswhich are present as said mixture, wherein said polyvinyl alcoholhas a degree of hydrolysis greater than 98.0%, and wherein water-solublesalt content is not over 1.0%.

9. A dry mixture of polyvinyl alcohol and starch adapted for admixturewith Water to form stable size or adhesive compositions, consistingessentially of:

(a) a polyvinyl alcohol having a degree of polymerization ranging fromabout 300 to 1400 and a degree of hydrolysis greater than 95%; and

(b) a modified starch consisting essentially of starch containing COOXgroups, wherein X is a cation selected from Na K+, or NHJ, in the amountof 0.3 to 3% by Weight based on said modified starch of -COONa, or molarequivalent of COOK or COONH said COOX groups being present asstarch--OCH COOX, or as a mixture of and starchCOOX, said mixturecontaining at least 0.1% COONa, or molar equivalent of COOK or COONH asstarchOCH -COOX, said modified starch being further characterized by analkali fluidity of less than 95 and above 5 and by being substantiallyfree of inorganic salts; said mixture containing at least parts byweight of said polyvinyl alcohol per 90 parts of said modified starch upto 60 parts of said polyvinyl alcohol per 40 parts of said modifiedstarch.

10. The mixture of claim 9 wherein said COOX groups are COONa groups andare present as said mixture.

11. A dry mixture of polyvinyl alcohol and starch adapted for admixturewith water to form stable size or adhesive compositions, consistingessentially of:

(a) a polyvinyl alcohol having a degree of polymerization ranging fromabout 300 to 1400 and a degree of hydrolysis greater than 95%; and

(b) a modified starch dispersed in said carrier consisting essentiallyof starch containing COOX groups, wherein X is a cation selected from NaK+, or NHJ, in the amount of 0.4 to 2.0% by Weight based on saidmodified starch of COONa, or molar equivalent of COOK or COONH said COOXgroups being present as starchOCH COOX, or as a mixture of starch-OCHCOOX and starch-COOX, said mixture containing at least 0.2% of COONa, ormolar equivalent of COOK or COONH as starch-OCH COOX, said modifiedstarch being further characterized by an alkali fluidity of 30 to 90 andby water-soluble salt content of less than 1.5% by Weight; saidformulation containing at least parts by weight of said polyvinylalcohol per 85 parts of said modified starch up to 50 parts of saidpolyvinyl alcohol per 50 parts of said modified starch.

12. The mixture of claim 11 wherein said COOX groups are COONa groupsand are present as said mixture, wherein said polyvinyl alcohol has adegree of hydrolysis higher than 98.0%, and said Water soluble saltcontent is not over 1.0%.

13, A compatible, stable formulation of polyvinyl alcohol and starchconsisting essentially of:

(a) an aqueous carrier;

(b) a polyvinyl alcohol dissolved in said carrier having a degree ofpolymerization ranging from about 300 to 1400 and a degree of hydrolysisgreater than 95%; and

(c) a modified starch dispersed in said carrier consisting essentiallyof starch containing COOX groups, wherein X is a cation selected fromNa+, 10', or NHJ, in the amount of 0.4 to 2.0% by weight based on saidmodified starch of COONa, or molar equivalent of COOK or COONH said COOXgroups being present as or as a mixture of starchOCH CH COOX andstarch-COOX, said mixture containing at least 0.2% of COONa, or molarequivalent of COOK or COONH as starch0CH CH COOX, said modified starchbeing further characterized by an alkali fluidity of 30 to 90 and by awater-soluble salt content of not over 1.0% by Weight; said formulationcontaining at least 15 parts by Weight of said polyvinyl alcohol perparts of said modified starch up to 50 parts of said polyvinyl alcoholper 50 parts of said modified starch.

14. A dry mixture of polyvinyl alcohol and starch adapted for admixturewith water to form stable size or adhesive compositions, consistingessentially of:

(a) a polyvinyl alcohol having a degree of polymerization ranging fromabout 300 to 1400 and a degree of hydrolysis greater than 95%; and

(b) a modified starch dispersed in said carrier consist ing essentiallyof starch containing -COOX groups, wherein X is a cation selected fromNa K or NHJ, in the amount of 0.4 to 2.0% by Weight based on saidmodified starch of COONa, or molar equivalent of COOK or COONH said-COOX groups being present as starchOCH CH -COOX, or COONH as starchOCHCI-I -COOX, and starch-COOK, said mixture containing at least 0.2% ofCOONa, or molar equivalent of COOK or C'OONH as starchO CH CH XC OOK,said modified starch being further characterized by an alkali fluidityof 30 to and by water-soluble salt content of not over 1.0% by Weight;said formulation containing at least 15 parts by weight of saidpolyvinyl alcohol per 85 parts of said modified starch up to 50 parts ofsaid polyvinyl alcohol per 50 parts of said modified starch.

References Cited UNITED STATES PATENTS 2,808,380 10/1957 Olsen et al26017.4 ST 3,652,541 3/1972 Hjermstad et a1. 26017.4 ST 3,652,542 3/1972Hjermstad et a1. 26017.4 ST

HAROLD D. ANDERSON, Primary Examiner E. WOODBERRY, Assistant ExaminerUS. Cl. X.R. 117l55 UA @7353? I UNITEDSTATES PATENTDFFICE 1 VCERTIFIQATE OF CORRECTION Patent No. v ,757,606 I Datod October 23, 1973xnvemogs) \ERILINIG T. H dERMST AD-ot' a] It is.cert'ified that errorappers in the above-idntified patent and that said Letters Patent arhereby corrected as shown below:

' In Column 12, Line 42 now reads "or -C0ONH as starch-O- CHZCHZXCOOKJ;this shouldrread or, .I-COONH4, as tarch-o-cu cn -cooxr Signed and sealTod this 12th dayfof March 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR., c; MARSHALL DANN Attestlng Offlcor Commissionerof Patents

